No photos tonight, nothing to really see. I tore the stab apart, got the reinforcement and splice angles primed, then finished final-drilling the spar channels and dimpling the necessary holes. Everything is now prepped and ready for riveting!

So tonight I finished up the last bit of major fabrication for this SB/repair job. I initially had some car-related stuff to do after I got home, but still found an hour to spend out in the shop.

Tonight’s job was fabricating the “replacement” forward flanges for the inboard main ribs. The addition of the doublers on the aft side of the spar necessitates this, since the original flanges used to mate with the spar channel. The new flanges are made of angle material, which are riveted to the rib web. Normally the four attach holes would be drilled in assembly with the spar, using the existing rib attach holes, but since I’m starting over, I don’t have all of those. I do have the two “inner” holes, which are where the the forward inboard ribs attach, and which I drilled last time. The “outer” holes, though, I get to lay out myself.

Anyway, to start with, the angle pieces are clamped to the ribs and the ribs clecoed in place in the stab assembly. Then the angles need to be carefully slid forward to mate tightly with the spar. This means loosening those clamps while still maintaining the vertical positioning of the angle. Next, the angles need to be clamped tightly to the spar prior to using the two existing holes to drill.

The end result is kind of a mess of clamps, and sort of difficult to get a photo of. To the left is the rib, to the right is the spar, and sort of barely visible in the middle is the angle:

With those two inner holes drilled in each angle, they’re now positively located to the spar, and the ribs can be removed to better show the assembly:

Now comes the more fun part: figuring out where the two outer holes need to be located. These holes will go through four pieces: the rib angles, the doubler, the spar channel web, and the reinforcement angles – and I need to make sure I maintain good edge distance on all of those. Really, the only items of serious concern here are the angles. To make it easier to do this layout, I decided it was best to disassemble the angles and doublers, then cleco those items (minus the spar channels) on the bench to be able to better visualize things. With that done, it was easy to use a straightedge to trace the inner edges of the reinforcement angles onto the rib angles:

Then it was easy to lay out the desired rivet locations, center punch them, and drill a #40 pilot hole in each location. Then I was able to cleco all those pieces back together with the spar, and use those pilot holes to final-drill #30 through the entire assembly. With the rib angles fully fitted to the spar, I could now cleco the ribs back in place and get ready to drill the rivet holes between them and the angles.

Once the ribs were in place, I clamped each rib to it angle with two small C-clamps. The C-clamps were the right tool for the job, as I need these things to be clamped super tightly. Once the clamping was done, the rib and angle was unclecoed and removed as a unit, so I could drill the pilot holes (already in the rib) to final size in assembly with the angles.

The pieces clamped and ready for drilling:

And the pieces all drilled and ready to go:

And that’s it for the fabrication stuff. There’s still some disassembly, demurring, dimpling, and priming to be done, but overall I’m pretty close to being ready to start riveting all this stuff back together!

Good solid day of work, sprinkled in between the usual weekend stuff. I started off this morning by finishing all the drilling on the spar assembly, using the prepunched holes in the doublers and angles to drill through everything. Took everything apart to deburr and then double-checked the edge distance on the doublers – all good!

Next up was figuring out how to fit the inboard ribs. Here I was going to be inventing my own procedure, since I already had pre-fitted ribs, and I’d need to use those to lay out the rivet holes through the spars. I figured the way to go here was to cleco the skins to the underlying skeleton, and essentially treat this entire procedure as if I was back to performing the service bulletin on a fully-assembled stabilizer. So I broke out the bucket of clecos and got to work. Now we’re back to something resembling an airplane part:

At this point, I had the inboard nose ribs in place, but not the main ribs, and here I ran into my first bit of challenge. The new spar channels are only partially prepunched where they met with the skins – only outboard of the center ribs (this is why the span wise line of clecos above stops halfway in). The problem was, that meant the inboard portion of the spars wasn’t clecoed to anything, and the result was that it didn’t sit flush against those inboard nose ribs:

This is an issue, since I’m going to use those holes in the nose rib flange to locate and drill the rivet holes through the spar assembly. I need all this to fit tightly together. So I had to get creative and figure some way to pull the spar forward to get it tight against that rib flange. It wasn’t too hard, nothing that couldn’t be solved by a long clamp applied in a super precarious manner:

Drilling was fun with this setup too, since that clamp kind of got in the way of accessing that rear flange. I’d originally intended to use the angle drill to make these holes, but it was impossible to get it perpendicular to the surface because the rib web was so close. So I ended up doing things in two stages: I started the holes using a 12” #30 bit, but didn’t go all the way through. I was thinking of how I enlarged those holes in the old spar doing something similar to this, and I was more concerned about that since it can be hard not to apply a side-load to the long bit. I drilled just deep enough with the long bit to get a good start on the hole, then removed each rib and finished the holes using the angle drill. It was a bit painstaking, but it got the job done.

Here we are with both of those rear flange holes complete:

That wasn’t the end of the challenge, though. Next I’ll need to fit the aft inboard ribs, including the piece of aluminum angle that will be spliced in to act as the replacement front flange. To fit this properly, I can’t have those clecos sticking through the holes in the spars, but I still need the spar to fit tightly against the nose ribs for the fitting to work right. So I decided this was the time to final-drill those spar holes in common with the skin. With those done, I was able to remove the nose ribs and still have the spar stay in place, since those holes in common with the skin now positively locate the spar.

My last act of the night was to take the piece of angle material provided for the splice flanges and cut off two 2 15/16” pieces. I cleaned the cut edges up on those and then set them aside – I’ll pick up with that bit of work tomorrow night (or maybe Tuesday). Properly locating these splice angles will require some care, especially since I’ll be inventing my own method for locating the holes. But once that’s done, I’ll be finished with major fitting, and I can move on to some final prep work – final-drilling a few more holes, dimpling the spar, and priming the pieces that need it – and then it’s on to riveting this thing back together.

The end (of this little side journey) is in sight!

Busy day. Had a fly-out event for work in the middle of the day, then another thing in the afternoon. Still found some time to get out in the shop, though.

Tonight was almost entirely just doing modification work on the spar channels. The big fun here is cutting the relief notches at the spot where the channel will be bent to match the bends in the angles. I’d read about people having edge distance issues here, so before I cut anything, I cleaved both the angles and the doublers to the spars, and marked the holes in each piece that would eventually be drilled into the other piece. The important bit here is that a couple of rivet holes for the doublers end up really close to the relief notches. And I found that if I had naively cut the notches as called out in the plans, I would have violated minimum edge distance here.

With that in mind, I laid out the notches so they wouldn’t be so deep. Unlike the SN notches – which are made entirely by hand with a file – here the main work is done with the drill, ending in making a 1/4” hole with the unibit. Next the corners of the flanges get trimmed, and the whole area gets some sculpting with various files to make everything nice and smooth and round.

By the book, the next operation would have been bending the spar tabs, but I decided it’d be smart to go ahead and clean up the edges of the spar channels first, so that’s what I did. Then I carefully marked the bend lines and made the bends. Then I clecoed everything together for a test fit:

The interesting part now is this: Earlier, I was supposed to have drilled all the holes inboard of those bend lines, while the other holes were to be postponed until after the bends were done. But at no point do the instructions actually say to drill those holes…guess I’ll go ahead and do them, there’s no reason not to now that I can see.

The other fun thing I noticed tonight: the spar channels are not fully prepunched where they mate with the skins. For whatever reason, they only seem to be prepunched outboard of the mid-span ribs. So it appears I’m going to have to drill all of those holes in assembly with the skins when I temporarily put this together in the near future.

The other real fun will be fitting the inboard ribs. I’ll have to think hard about how I’ll locate the top and bottom rivet holes for the inboard main ribs. The two center holes are made in assembly with the nose rib, so those locations are predetermined. The other two holes – well, with the forward flanges of the main ribs gone, there’s nothing to match up with, so I guess in a certain way of thinking I can put them wherever I want…eh, we’ll see.

So with new parts in hand, I got right to work this evening. It was a good night for it, too – some rain during the day today seems to have dropped the temperature nicely.

The funny thing is, I waited until today to work on this so I could print out the updated construction manual pages, and then I proceeded to mostly ignore them today. They seem to be kind of inaccurate, actually – for example, they speak of drawing rivet lines on the doublers to help lay out the holes, but the doublers I got are already almost totally prepunched, so there’s no leeway to play with spacing here.

With that in mind, I decided to start by drilling the reinforcing angles to the spar channels – at least the center holes, inboard of where the channels will get bent to match the sweep of the spar. Doing this meant I had the holes in place that I needed to cleco the doublers and the v-stab splice plate in place to see how everything fit together. As you’d expect from prepunched parts, there was no interference between anything.

Next, I removed the reinforcement angles and marked the required tapers on their ends, then made the tapers. I rough-cut on the band saw, cleaned up the long cut lines with a vixen file, and then used the scotchbrite wheel to round the corners and clean everything up.

With that done, I got to thinking about how I could verify that I’d have good edge distance on the new doublers. Seeing as how they’re prepunched, I figured they ought to be fine, but since I’m rebuilding after ruining the old spar, I’m feeling a bit conservative with this stuff. The only holes that aren’t prepunched in the doublers are those in assembly with the inboard ribs, and those that will match the outboard holes the angles (outboard of the bend line). Those outboard holes aren’t prepunched in the spar; they get drilled in assembly with the angles. That meant I couldn’t easily mark the prospective hole locations on the doublers either…hmm.

Then it hit me…I could just cleco the angles to the splice plate and doublers, without the spar involved. The alignment wouldn’t be precisely the same as when everything is together, but it’d be plenty good enough for verifying the edge distance. And it was super easy to do:

So I marked the holes, disassembled everything, and then marked an edge distance line around the perimeter of the doublers. The results are not really what I’d hoped for, though. The holes on the bottom are OK, but the top is a different matter. The inboard holes are slightly out of spec, but the outboard ones are way worse. The edge distance lines drawn here shouldn’t overlap the edges of the holes:

So now I get to decide how to handle this. I can only think of two real options: first, accept the edge distance as it is and build on. Second, try and modify the upper angle a bit to tweak the holes downwards. That second option actually isn’t as wacky as it sounds at first. The angles already have to be bent to match the swept portion of the spar – I could maybe apply the mallet to bend the “ears” down a bit to migrate those holes. It wouldn’t take much at all, really…but it is still finagling with a kind-of important structural piece.

And of course I had to hit this on a Friday night, when there will be no Van’s support available until Monday. I guess I’ll start by asking around on VAF and see what kind of stuff I hear. I really don’t want to stop work for the weekend…

UPDATE: Actually, this isn’t as bad as I thought. The common rule of thumb for rivet edge distance is 2x the rivet diameter to the hole center, or 1.5x the diameter to the edge of the hole. However, a closer look at the mil-specs provides a more precise number…specifically, for 1/8” rivets, the minimum distance to the hole center is 0.219”, or about 7/32”. Using that number, and measuring with my calipers (much more accurate the two sharpie lines), I’m find on edge distance everywhere except the inboard most hole on that top angle, and in that case it’s barely out of spec. With that in mind, I’m going to build on.

Not logging this as any actual time tonight since it was mostly 15-20 minutes of tinkering around…but today my nice care package from Van’s arrived. New spar channels, reinforcement angles, doublers, and some assorted hardware. The one thing I forgot to do was to print out the updated h-stab assembly instructions at work today. I have toe up-to-date manual on my laptop, but I want a hard copy to refer to while I work. I think I have a decent handle on the procedure, but I’d rather not wing it since I’m already rebuilding.

So all I did tonight was cleco some random stuff together and take a look at test-fitting the various parts. Interestingly, the doublers that come with the new kits appear to be different from the doublers that I got with my SB kit. The overall shape is the same, but they have a lot more prepunched holes. I can only assume this is a slight difference between new-construction and retrofit procedures.

Anyway, I’ll see about picking up with some actual work tomorrow evening.

Nothing exciting to report today, no awesome photos or anything. Just drilled out a bunch more rivets and got the right half of the stab torn down. Overall I’ve been happy with how this went, drilling out the rivets was surprisingly painless and fast, and while there are a few holes that will need some attention when I reassemble, I didn’t mangle any more parts.

So that’s about it – I’ve got a pile of parts now, and I’ve just got to wait for the new stuff to come in later this week. Then I get to remember how to build this thing…

As usual, lots of other stuff going on today, including the monthly Houston RV lunch, which went pretty long since we had some out-of-town guests in attendance. But I made good progress on disassembly.

My initial plan for the spar replacement was to only partially disassemble the stab. I was figuring on leaving the forward main rib in place, and maybe the tip rib as well. It seemed easy to only remove what I absolutely had to to get that forward spar out. I started the morning by drilling out rivets on the aft main rib; in my initial plan, the next step would have been to drill out the blind rivets attaching that rib to the spar and the forward main rib. However, after looking inside the skin at this blind rivets, I started to reconsider:

Getting to those was going to be a bit of a pain, and it seemed like a good opportunity to do more damage while trying to get at those rivets. At this point, I’d gotten pretty comfortable with drilling out skin rivets efficiently, so I decided it was only a tiny bit more effort to just go ahead, drill out everything, and completely disassemble the stab. So that’s what I did. After an hour or so of work, I was back just a bare skin for one half of the stab:

Drilling out those blind rivets was far easier with this piece of skeleton liberated from the skin. And so now, the left half of the stab is completely broken down. Tomorrow, I’ll repeat this process for the right half of the stab. I think I might be able to get it done in about an hour.

It’s been kind of surprising how painless this disassembly has been. I’d expected to invest a lot more time in this. Looks like I’m going to have to figure out something else to work on once this is done and I’m waiting on the new parts. I have a couple items in mind, though…

Finally got started on tearing this thing apart tonight. Over the past few days, I spent a fair amount of time thinking through this process. The main outcome of this was that I decided to go ahead and order my replacement parts after all, rather than waiting until after disassembly like I said last time. I figured it’d be better to get the parts in hand sooner, to minimize downtime. I can find other things to do while waiting on stab parts, but I’ll be limited in what I can do some I’ll have a workbench full of stab parts.

I also decided not to go ahead and replace the inboard ribs after all. After reviewing the stab assembly procedure, I was reminded that those ribs don’t come predrilled, and have to be drilled in assembly with the skin. That seems like an opportunity to cause problems, as well as being more work, so I’m going to use the ones I have – after all, there’s nothing wrong with them

Anyway, all that stuff shipped today and should be here middle of next week. In the meantime, back to disassembly.

My basic plan here is to reverse the assembly procedure – first, drill out all the rivets to the rear spar and extract it, then drill out the rivets between the skin and ribs and remove those, and finally remove the front spar. Tonight I figured I’d just see how far I could get on the rear spar. The answer was “pretty far.” I started by drilling out the solid rivets securing the structure together. Then there were the four Cherry blind rivets that secure the rear spar to the center ribs. Getting the heads off those was surprisingly easy, I was kind of expecting some drama, but it didn’t happen.

Next were the skin rivets.I got all these drilled out and removed fairly efficiently – instead of my usual painstaking three-step process, this time I just center-punched and drilled, being careful to try and keep the drill centered. It didn’t go perfectly, but I got all the rivets out without any major damage. There are a couple holes where I may need to go to a NAS oversize rivet, but mostly things went great.

At this point, I was ready to extract the rear spar, declare victory for the night, and retire inside. Except I couldn’t seem to get the spar to come out, it seemed hung up in the middle of each side. Right…oh, right where I took the heads off those Cherry blind rivets. The shafts of those rivets were still in place, and once I thought about it…of course they’re probably still holding things together, the whole idea with them is that they grip the sides of the hold really well. “Shaft” is really not a great word, what’s actually left is just a thin metal tube. One of them had its edge bent a bit, and I was able to get a punch on that one and drive it through, at which point that part of the spar got looser. That confirmed my theory – I just need to knock out the other three shafts. Well, first I need to figure out how.

I started trying to use a punch to catch the edge of the sleeve in one hole, then thought about the possibility of damaging the hole. I also thought about how I might be bending the rib flange inside the stab by doing this – I should really be backing that up with a wood block or something. The bottom line was that rather than trying to force this issue, it was better to just call it a night, let the problem marinate in my head, and revisit it tomorrow.

So that’s what I did. I’m happy with the progress I made today, even if it was sort-of backwards-moving progress. Tomorrow we’ll keep it going.

Update: I got the spar off after all. It suddenly occurred to me that all I needed was something to use as a punch that would fit snugly in the rivet hole. I didn’t have an actual #21 punch, but I did have a #21 drill bit. And it did a bang-up job of driving the rivets right out. Easy peasy.

Well, this isn’t the most pleasant post to write, but it’s the way things are. Upon reviewing the work I’ve done so far on this service bulletin, the long and short of things is that I’ve ruined some parts and I’ll be substantially rebuilding the horizontal stab.

I mentioned in the last post that I’d had a few holes that got enlarged in the spar web, due to using a dull bit in the angle drill. At that time, I figured I could just replace those with 5/32” rivets and be fine. But I took a closer look at those holes tonight, and while two of them that are oversize can be safely opened up, the other two are far too large. I thought briefly of asking Van’s support about the possibility of doing another doubler repair here, but some reading on VAF reveals other builders who have gotten some very direct guidance on this topic, and that guidance is that any hole that can’t be fixed by opening up to #20 calls for replacement of the spar. Since I damaged both spars, I’ll be replacing both of them.

There are also some edge distance and hole spacing issues with the doublers I drilled, but that’s kind of beside the point right now, as the doublers will need to be re-drilled with the new spars anyway. While I’m at it, I’m also going to replace both reinforcing angles and all four of the inboard ribs. This is basically all fo the inboard/center structure in the stab. It’s possible that the ribs could be salvaged, but at this point I figure I might as well go all-in on using post-SB parts.

At the moment, my plan is to hold off on ordering anything until after I’ve done all the disassembly required for this replacement work. This is to allow for the possibility of damaging other parts beyond repair; better to make one parts order instead of two. I thought about going ahead with that disassembly work tonight, but I think it’s better that I take the rest of the night off and let this sink in before jumping into more work.

The good news is that the financial damage isn’t horrible. Replacing the parts listed above will cost about $140. Things only start getting significantly more expensive if I have to replace parts of the rear spar or the skins. I don’t think saving the rear spar will be a problem, but the skins might be a different matter – there are a lot of rivets to drill out carefully. Then again, my fancy new rivet removal tool will hopefully make this go better.

At this point, I think my goal will be to complete disassembly by the end of this weekend, and order the parts early next week. A stretch goal might be to get disassembly done tomorrow night and order the parts Friday, that’d save me a few days waiting, but again, rushing disassembly is likely to just make things worse.

Anyway, that’s it for tonight.